Patek Philippe's perpetual calendar chronograph history runs in a fairly straight line from the 1518 through the 2499 to the 3970 and beyond, with every one of those models being round. Then there's the 5020. Launched in 1994 as a companion to the 3970 rather than a replacement, it took the same complication set and wrapped it in a cushion-shaped case that collectors quickly nicknamed the TV Screen. It's still the only perpetual calendar chronograph Patek has ever made without a round case.